Corrected MapParams Behavior to Avoid Unintended Filtering

[raphael]

This PR addresses a bug in the MapParams DSL function. The issue stemmed from an unintended behavior where MapParams was filtering query string parameters based on their prefixes.

Clarification of the Issue:

In the existing implementation, consider this design:

var _ = Service("exampleService", func() {
    Method("exampleMethod", func() {
        Payload(func() {
            Attribute("id", String)
            Attribute("query", MapOf(String, String))
        })
        HTTP(func() {
            GET("/resource/{id}")
            MapParams("query")
        })
    })
})

The intention here is for MapParams("query") to map all query string parameters to the query attribute in the payload. However, due to the bug, the function was incorrectly filtering these parameters. It was only including parameters named like query[foo] or query[bar], and excluding others.

The PR Fix:

This update corrects MapParams to function as intended: it now maps all query string parameters, irrespective of their naming or prefixes, to the designated map attribute in the payload. This behavior distinguishes MapParams from Param, which is specifically used for filtering and including named query string parameters.